As a method for calculating a target throttle opening degree to be given to an electronically controlled throttle, there is known a method that uses an inverse model of an air model. An air model is a dynamic model that expresses a dynamic relation established between a throttle opening degree and an intake air quantity. If the inverse model of an air model, that is, an inverse air model is used, the throttle opening degree that is required to achieve a target intake air quantity can be inversely calculated.
The calculation method of the target throttle opening degree with use of an inverse air model also can be applied to an internal combustion engine with a supercharger. Note, however, in an internal combustion engine with a supercharger, the pressure that acts on the upstream side of the throttle changes in accordance with the supercharging state of the supercharger. A throttle upstream pressure is an important parameter that is used in calculation of a target throttle opening degree in an inverse air model. Therefore, in calculation of the inverse air model for an internal combustion engine with a supercharger, the supercharging pressure measured by a supercharging pressure sensor or the supercharging pressure that is estimated by a physical model is used as the throttle upstream pressure.
According to the method for calculating the target throttle opening degree by using an inverse air model, even when the target intake air quantity changes, the throttle opening degree that is required to achieve it can be calculated with high precision. However, in the calculation using the inverse air model that is a dynamic model, the target throttle opening degree which is an output value significantly changes with respect to a change of an input value. Therefore, there is a possibility of the target throttle opening degree to be given to the electronically controlled throttle being out of the appropriate range which is set in advance, depending on the condition of the input value. In particular, in the case of the inverse air model of an internal combustion engine with a supercharger, there is a fear that some sort of problem occurs to the supercharging pressure which is inputted. For example, when the supercharging pressure is measured by a supercharging pressure sensor, there is a possibility that the measured value of the supercharging pressure becomes inaccurate due to the problem of the supercharging pressure sensor (for example, wire breakage, deterioration of the sensor element, or the like).
It is not preferable in the control performance of an internal combustion engine that the target throttle opening degree to be given to the electronically controlled throttle is out of the appropriate range which is set in advance. Therefore, the controller of an internal combustion engine, in particular, the controller of an internal combustion engine with a supercharger is required to always monitor whether the target throttle opening degree is not out of an appropriate range.